This invention relates to a control system for frying apparatus. More particular, this invention concerns a thermstat control system for regulating and limiting the temperature of heating elements during cooking and pyrolytic cleaning cycles.
In deep fat frying system the electric heating elements often become coated with residues from the oil and cooked products after prolonged cooking periods. Cleaning the elements by hand is quite tedious and time consuming. Thus, the practice of burning off the elements, called pyrolytic cleaning, is sometimes employed. In pyrolytic cleaning the heating elements are raised to relatively high temperatures, usually between 600.degree. and 900.degree. F. Above about 1000.degree. F. the burner elements may discolor and oxidize, possibly resulting in permanent damage to the elements. Moreover, pyrolytic cleaning has been found to be safer and more effective if the temperature of the elements is raised gradually to allow slow burn-off to occur and decrease the possibility of damage to the heating elements and associated apparatus.
During cooking, malfunctions of the operating thermostat may cause overheating of the cooking fluid resulting in burning of the product, premature deterioration of the cooking fluid and even flash burning of the fluid. Thus, the cooking fluid temperature must be maintained below a safe temperature limit, usually about 475.degree. F. in order to insure a safe and efficient cooking operation.
The present invention concerns control apparatus for use in fyring systems to regulate and limit the temperature of heating elements during cooking and pyrolytic cleaning. A first control circuit is provided for maintaining the temperature of the elements below a first predetermined cooking limit. A second control circuit maintains the temperature of the heating elements below a second predetermined limit during pyrolytic cleaning of the elements. A function switch selectively connects said first control circuit or said second control circuit to the heater elements depending upon whether cooking or pyrolytic cleaning of the elements is desired.
In another aspect of the invention, a high-limit cooking thermostat is connected to a frypot heater to limit the cooking temperature of the heater. A high-limit burn-off thermostat is connected to the heater for maintaining the temperature of the heater below a higher temperature during pyrolytic cleaning. A switch operates to bypass the high-limit cooking thermostat during pyrolytic cleaning to allow the heater to rise to the higher temperature before being disconnected by the burn-off thermostat.
In accordance with a further aspect of the invention, identical first and second high limit thermostats are attached to heating elements in a frypot. The heating elements operate in cooking fluid during a cooking phase and can be raised out of the fluid and burned off during a pyrolytic cleaning phase. The first and second thermostats are both connected into the heater circuitry during the cooking phase in cooking fluid, and are set to open above a safe operating temperature limit. The second thermostat remains in the heater circuitry during the pyrolytic cleaning phase and is set to open above a higher temperature limit. A percentage relay cycles the heaters off and on to slow the temperature rise of the heater elements during pyrolytic cleaning, thereby protecting the elements from damage and improving the efficiency of the cleaning process. A manual reset switch is provided to prevent automatic recycling of the thermostats after the predetermined temperature limits have been exceeded. A function switch automatically disconnects the first thermostat when the heating elements are raised out of the cooking fluid and automatically reconnects the first thermostat when the heating elements are returned to cooking position in the fluid.